I only know how to use the second model, the North America Model (NAM).
Click on any of the options (no idea what is the difference).
Click on "namer" for North America

Click, for example, on 500_vort_ht and then on Loop.
Check out the top line that tells you day and hour of the animation.
Note: the time is in UTC (subtract 7 hours for PDT - 1800 UTC = 11 am for us)
Focus on the map to see the contours of North America (the eye tends to focus on the moving lines)
Click on California (if that's what you're interested in) and keep clicking to zoom in the region you want to explore.
Or you can click on the various panels for details.
This map is showing what is going on in the atmosphere,
i.e. the closest thing to checking the weather on top of a mountain.

The yellow shading indicates upper level clouds and precipitation; darker means denser.

The arrows indicate wind direction; the feathers indicate speed.
One full feather equals 10 knots, a triangle equals 50 knots
(1 knot = 1.85200 km/h ).
The maximum wind you can tolerate on a hike is 60-70 km/h)

Next, check the 700_rh_ht model.
This map shows what is going on in the atmosphere at approximately 3000 meters.
That's usually the tree line.
Green shading indicates chance of precipitation.